Mac SE/30 Audio Visualizer

Sure, you could make it into a web server, but [markie] sent me his Mac SE/30 visualizer. It was inspired by another’s mac mod, but he was kind enough to write up an entire how-to. The audio signal was run directly into the deflection coils on the macs tubes. The mod is so simple, I might have to pick one up just for CRT experimentation.

[The next regular podcast cometh, but It’s delayed by my cold.]

24 thoughts on “Mac SE/30 Audio Visualizer

  1. You know, every time I see one of these mods (there has been at least one other posted here in the past), I always wonder how hard it would be to turn an old CRT into a basic oscilloscope. Certainly it would not be of any great accuracy, but it seems like it should be possible to put something together that could be at least marginally useful for the electronic’s tinkerer, and not cost $500.

    But really, since when did these hacks have to have a point in the first place? I would just like to see it done for the sake of doing it.

  2. Try rotating the yoke first! Now that’s a good idea. Proper left-right scan. I’ve built several of these. I’d recommend adding an amplifier of some kind, or at least a resistor, as the resistance of those deflection coils is around the 1 – 2 ohm mark I do seem to recall, and thus may damage your stereo machine.

  3. also, I doubt the CRTs in these things could kill a person. I got a minor shock off one once. Leaving it for a while after shutting it down should do the trick, and it’ll save you accidentally breaking the glass and experiencing an embarassing implosion.

  4. >I’d recommend adding an amplifier of some kind

    >as the resistance of those deflection coils is around the 1 – 2 ohm mark I do seem to recall, and thus may damage your stereo machine.

    There is an amplifier in this setup, I did take some old amp (I bought for 10 euros) dedicated for these Macs and not a ‘proper’ amp (in case I would break it) ;-) The resistance I measured is indeed 1-2 ohm.

  5. I’m guessing the mac has a constant operating high voltage supply, which is somewhat unusual… Most monitors and televisions use the energy from the collapsing field in the horizontal deflection coil as a power source for the high voltage supply. In these cases, it is generally required to leave the horizontal coil attached, and move it off to the side, using another coil for your deflection.

  6. Curious if this could be applied to any sort of CRT display of the instructions are specific to just this type of Mac. Very interesting, but alas, no room for a dedicated visualizer display… I’m sticking with the ol’ software vis.

  7. The fact that you used rubber gloves to protect yourself against the high voltage out of a tv really disturbs me. The output from a flyback transformer can easily break through most gloves, gloves that are designed to take 30kv have a very thick layer of rubber and a layer of cotton to protect the rubber.

    In any case, if it works it works ;)

    As to making one into a real oscilliscope, there are a few problems. The first is that you need a time base for the x-axis. You should be able to get away with a function generator that gives a sawtooth wave feeding into an amp for that tho… But the bigger problem is that the magnetic coils are very limited in their bandwidth, being highly inductive they can’t be used for more then a few hundred khz.

    Although a scope made out of a big ole TV would be a great teaching tool to show classes what waves look like…

  8. #7:
    Ha – “I doubt the CRTs in these things could kill a person”. The flyback transformer in that CRT puts out 20kv. The phosphorus in the front of the screen will kill you. And, think about what you are doing in a CRT; shooting electrons at near light-speed at a piece of phosphorus and glass. That uses a lot of power. Be careful, y’all.

    #6 You CAN make a CRT into an oscilloscope

    CRT’s rock.

  9. @ #14: sure, the vacuum, the phosphorus and the sharp edges could all potentially kill a person, but concrete will kill you if you eat enough of it….

    as for shooting electrons at “near light speed” – it doesn’t really use that much energy. electrons don’t exactly have a lot of mass. the voltage used to accelerate the electrons in a macintosh SE is quite high, but it’s quite low current. it probably wouldn’t be the best idea to touch it while it’s on, but once it’s been switched off it’s fairly safe very quickly. the large power filter capacitors on the analog board present more of a risk.

    anyway, don’t just take my word for it, this topic has been discussed to death on places like applefritter where turning compact macs in to interesting things is practically a way of life… and of course, as always, better safe than sorry :)

  10. I did the same thing about 15 years ago with two ancient IBM dumb terminals. The long-persistence green phosphor made for a very nice display. The cases were painted gray fleckstone, and they were a big hit at a mad-scientist themed Halloween party I hosted. I no longer have them, they were trashed one move because they were huge and weighed a ton. I tried again with a modern monitor, but I didn’t like it nearly as much without the long-persistence phosphor.

    Tip: make sure you don’t run the electron gun without either the X or Y deflection running, you’ll burn the screen. there will be a blackened spot and a permanent smoke trail running up the inside.

  11. #19: if you have nothing better to do than complain about how other people have nothing better to do then *you* need to reconsider your life ;)

    anyway i sold the se because it was broken and i was moving and i really didn’t care about it anymore :/

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